The applicants proposed to explore a design concept for the development of economic, compact PET (Positron emission tomography) systems (ezPET) which promise high performance at low cost, as well as excellent design flexibility and user friendliness. The key to the new design concept is the use of non-iterative sinogram restoration techniques for exploiting the full information content made available by the use of the new-generation depth-of-interaction (DOI) detectors. Using this design concept, the goal is to develop PET systems that employ detector rings as small as their intended sizes of the field-of-view (FOV), but produce images of ultrahigh resolution ( aboutl mm) free of parallax errors with no need to resort to interactive reconstruction methods. In this research, the applicants propose to build a prototype benchtop unit for verifying the proposed design concept. This benchtop unit will also be used to examine various important design issues, including the selection of detector-ring radius for given FOV size and the effect of DOI-detector configuration on achievable image quality. In addition, they will also measure the system sensitivity, scatter fractions, and noise equivalent counts for various system configurations. From these measurements, they will form important design guideline and utilize them to design an ezPET system specifically for imaging small animals. Thus, the proposed ezPET systems will facilitate the penetration of PET technology into community hospitals as well as a wide area of biomedical research.